Cooled screw vacuum pump

ABSTRACT

A cooled screw vacuum pump has a housing ( 4 ) two rotating systems ( 5, 6 ) consisting each of a screw rotor ( 5 ) and a shaft ( 6 ), a floating device supporting the rotors having, on each shaft, two mutually spaced bearings ( 7, 8 ) and an empty space ( 31 ) arranged in each rotor ( 5 ) open on the bearing side, wherein is respectively located an element cooling the rotor internally. In order to improve cooling it is suggested that the bearing ( 7 ) of the support located on the rotor side, is placed outside the rotor ( 5 ) empty space ( 31 ), such that in said empty space ( 31 ) there is more room available for obtaining efficient cooling.

BACKGROUND OF THE INVENTION

The present invention relates to a cooled screw vacuum pump comprisingtwo rotating systems, consisting each of a screw rotor and a shaft witha floating device supporting the rotors, having, on each shaft, twomutually spaced bearings and an empty space arranged in each rotor, openon the bearing side, wherein is located an element cooling the rotorinternally.

In an already proposed screw vacuum pump of this type, the bearing ofthe floating support on the rotor side is located within a centralhollow space, open toward the bearing side, inside the rotor. Cooling iseffected with the aid of a lubricating oil, which is first passed,inside a central channel in the shaft, to the bearing on the side of therotor. In known fashion, the transported oil volume is larger than isneeded for lubrication of the bearing in order to be able to carry awaythe maximum amount of heat possible.

With respect to the screw vacuum pump, the oil volume which, accordingto the state of the art, can be passed through the empty space, islimited since it is not only the bearing but also the bearing supportthat must be accommodated in said empty space. Therefore, there is therisk of inadequate cooling on the pressure-side region of the screwvacuum pump since it is precisely in this region that the generated heatis greatest due to the executed compression work.

Because of the existing empty space inside the rotor, the wall thicknessof the rotor is also limited in the bearing region of the empty space.As a result, it is only possible at very high temperature gradients, tocarry off the heat developing in the pressure-side region of the screwthreads via the suction side region of the rotor, the shaft and thecooling oil. High temperature or inadequate cooling of the pressure-sideregion of a screw vacuum pump results in uneven rotor expansions andthus in local clearance consumption between the rotors and between eachof the rotors and the housing. Run-up of rotors may, in fact, beprevented by relatively large clearances.

Relatively large clearances, however, result in deterioration of thepump operating properties. Furthermore, with respect to the prior knownscrew vacuum pump, there exists the danger of overheating the bearinglocated in the empty space, all the more so since said bearing can onlybe lubricated with relatively warm oil. Finally, the prior known screwvacuum pump can only be operated with vertically arranged shafts.

The present invention is based on the object of equipping a screw vacuumpump of the initially mentioned kind with improved cooling means.

According to the invention, this object is solved by making use of thefact that the bearing on the rotor side of the support is locatedoutside the empty space in the rotor. The invention facilitateseffective cooling of the rotor from the inside without being impeded bythe bearing and bearing support, so that the unwelcome clearanceconsumption will no longer occur in this critical region.

Each rotor appropriately consists of two segments with different threadprofiles, whereby the thread depth of the pressure-side segment issmaller than the thread depth of the suction side segment. A lesserthread depth in the pressure-side segment provides more space foraccommodation of the empty space needed for the internal cooling.

If, in addition, the rotor and housing are stepped in such manner thatthe pressure-side rotor segment has a smaller diameter than thesuction-side rotor segment, then this measure creates more space in thehousing for the accommodation of jacket cooling.

According to another characteristic of the invention, it is appropriateto additionally provide in the wall of the pump housing, i.e at least atrotor level, channels perfused by a cooling agent.

A cooling agent of this type permits, specifically in combination withthe interior cooling of the rotor according to the invention, uniformtempering of the entire pump. Consequently, the pump is able to adoptvariable temperatures with variable loads, without resulting in gapreductions. It is appropriate to also include in such tempering thebearings, the bearing supports and the driving motor, in order toprevent problems due to variable temperature expansions. Lastly, ajacket cooling of the proposed type has the benefit of having the effectof excellent sound deadening.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take form in various components and arrangements ofcomponents, and in various steps and arrangements of steps. The drawingsare only for purposes of illustrating a preferred embodiment and are notto be construed as limiting the invention.

FIG. 1 is a section through a screw vacuum pump with cooling accordingto the invention; and

FIG. 2 is a partial section according to FIG. 1 with an additionaldesign for cooling according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 1, a section through an exemplary embodiment of ascrew vacuum pump 1 according to the invention is depicted, i.e. at thelevel of that of the two rotating system which is equipped with adriving motor 2. Synchronization of the two rotating systems is effectedwith the aid of toothed wheels 3.

The rotating systems, which are arranged in housing 4, each comprise arotor 5 and a shaft 6. Each rotor 5 is overhung, in other words,unilaterally supported. The shaft 6 supports itself in a housing 4 viabearings 7 and 8 and also bearing supports 11 and 12. Frontally, housinglids 13 and 14 are provided, with lid 13 on the rotor side beingequipped with an inlet stub 15. Bearing support 12 is a component of thegear-side lid 14.

The rotor 5 consists of two positively joined rotor segments 17 and 18having different profiles 19 and 20. The suction-side rotor segment 17has a large volume profile 19 in order to achieve high volume flows in ahelical compression chamber. The pressure-side segment 18 of rotor 5 hasboth a reduced profile volume as well as a lesser diameter. This reducesthe cross section of the helical compression chambers or pumpingchambers 49. Internal compression is obtained, and the work done oncompression is reduced.

The inner wall of housing 4 is adapted to the rotor gradation (Gradation21). A dotted line 22 indicates that the housing may be designeddivisible at the level of gradation 21. As a result, it is possible toreplace the suction-side rotor segment 17 and the suction side element4′ of housing 4 with rotor segments having different profiles, lengthsand/or diameters as well as having housing segments 4′ adapted to same,in order to be able to adapt the pump to different applications.

The outlet of pump 1 which is adjacent to the pressure-side end of thethread turns is identified by the numeral 24. It is laterally conductedoutward. A housing bore 25 also issues into the outlet, joining thecompression chamber with the outlet at the level at which itscross-section decreases-either by gradation or by change in the threadprofile. In the housing bore 25, there is a non-return valve 26 whichopens with excessive pressure in the compression chamber andshort-circuits the suction-side thread turns of the rotor segment 17with the outlet 24. In order to seal the helical compression chambersfrom the support, shaft gaskets 27 are provided which are locatedbetween bearing 7 and the rotor segment 18.

The cooling system in the depicted exemplary embodiment comprises arotor with interior cooling arrangement and a housing jacket tofacilitate cooling.

For realization of the rotor interior cooling, the rotor 5 is equippedwith a hollow space 31, open toward its bearing-side. Said hollow spacemay extend through almost the entire rotor 5.

With respect to rotor 5, consisting of two segments 17 and 18, thedelivery or pressure-side segment 18 is appropriately designed hollow.The suction-side segment 17 closes the suction-side end of the hollowspace 31. The shaft 6, which is appropriately designed in one singlepiece with rotor 5 or with the pressure-side segment 18 of rotor 5, islikewise hollow (hollow space 32). In the hollow spaces 31, 32 there isa central cooling pipe 33, which is conducted, on the side of thebearing, out of the shaft 6 and ends, on the side of the rotor, shortlybefore the suction-side end of hollow space 31. The cooling pipe 33 andthe annular space formed by the cooling pipe 33 and the hollow shaft 6are available for the supply or removal of a coolant.

In the represented exemplary embodiment of the present invention, thebearingside opening 34 of the cooling pipe 33 is in communication vialine 35 with the outlet of a cooling agent pump 36. In addition, in theregion of housing lid 14 there is a coolant sump 37 in a coolant chamber50. Coolant sump 37 is connected via line system 38 with the inlet ofcooling agent pump 36. The sump 37 and the line system 38 are designedin such manner that the represented pump 1 can be operated in anyposition ranging from vertical to horizontal. Cooling agent levels whichoccur with horizontal and with vertical position of the pump 1 areindicated. Depending upon whether the cooling agent pump 36 is locatedoutside (as depicted) or inside (for example on the second, not visibleshaft of pump 1 at the level of the driving motor 2) of housing 4, theopening 34 of the cooling pipe 33 is located either outside or inside ofhousing 4.

For operation of the internal cooling of rotor 5, the cooling agent istransported by the cooling agent pump 36 from the cooling agent sump 37via the cooling pipe's inner surface or first channel 47 into the emptyspace 31 in rotor 5. From there, it flows back into sump 37 via theannular space or second channel 48 between cooling pipe 33 and shaft 6.The hollow space 31 is located at the level of the pressure-side regionof the thread turns of pump 1, so that this region in particular iscooled effectively. The cooling agent flowing back outside of thecooling pipe 33 along the second channel 48 tempers, among others, thehollow shaft 6, the bearings 7 and 8, the driving motor 2 (on thearmature side), and the toothed wheels 3, so that the thermal expansionproblems are reduced.

It is advisable for the cross section of the second channel 48 betweenthe cooling pipe 33 and the shaft 6 to decrease at the pressure end;this can be done, for example, by providing the cooling pipe 33 with alarger outside diameter in this area, As a result, a constructedpass-through opening or narrowed region 39 is formed. This constrictionensures that the spaces holding the coolant are completely filled.

It is advisable to select a material with poor thermal conductivity(such as plastic/special steel, etc.) for the cooling pipe 33. As aresult, the rotor 5 will be cooled more effectively, and the componentsof the pump 1 near the shaft will be tempered more uniformly.

The housing cooling system shown comprises cavities or a first and asecond set of channels 41, 42, respectively, in the housing 4. The firstset of cooling channels provided in the area of the rotor 5 aredesignated 41; the second set of cooling channels in the area of themotor 2 are designated 42.

One of the jobs of the cooling channels 41 in the area of the rotor 5 isto carry away the heat which develops especially on the pressure side ofthe rotor 5. Another job of the channels is to temper the housing 4 asuniformly as possible in the entire area of the rotor. Finally, thechannels are designed to give up the absorbed heat to the outside. Thechannels 41 through which the coolant flows therefore extend along theentire length of the rotor 5. The housing lid 13 serves to seal off thechannels 41 on the suction side. The housing 4 is also cooledeffectively on the pressure side.

Cooling channels 42, located at the level of the driving motor 2, havethe mentioned objects as well. They produce tempering of the drivingmotors (on the side of the coils) as well as tempering of the bearingsupport 11. Finally, they increase, to a significant extent, the thermaldischarge via the exterior surfaces of pump 1. The pump is appropriatelyequipped with fins 44, at least at the level of the cooling channels 41and 42.

Feeding the cooling channels 41, 42 with cooling agent is likewise donewith the aid of the cooling agent pump 36, namely via lines 45 and 46,if they are to be perfused parallel. Depending upon the thermalrequirements, there also exists the possibility of subsequentlyproviding same with cooling agent. One of the lines 45 or 46 could thenbe eliminated. The cooling agent gets from hollow spaces 41, 42 backinto the sump 37 via bores which are not represented in detail.

With vertical arrangement of shaft 6, the cooling agent located in thesump cools the bearing support 12, protruding into the sump 37. Withhorizontal arrangement, it is appropriate to let the returning coolingagent flow back over the internal side of lid 14, in order to cool boththe bearing seat 12 as well as improve thermal discharge toward theoutside.

In the depicted exemplary embodiment of the present invention accordingto FIG. 1, housing 4 and rotor 5 are—as already mentioned—designedpartable at the level of line 22. Consequently, there exists thepossibility of replacing the suction-side segments of rotor 5 (segment17) and housing 4 (segment 4′). Pump 1 can be adapted to variousapplications by installing rotor segments 17 with different profiles 19,different length, different pitch and/or different diameter, combined ineach case with an adapted housing segment. Various large profiles can beselected on the suction side in order to obtain high suction capacities,various long profiles on the suction side in order to obtain low endpressures and/or various volume gradations in order to obtain, forexample, higher fluid compatibility with lower gradation or with highergradation, high suction capacity with relatively small powerconsumption. Finally, there exists the possibility of providing, at thelevel of a reduction in the diameter of rotor 5, a circumferentialgroove in order to achieve, in certain applications, a release ofpressure in this region.

A cooling agent flowing through the screw vacuum pump 1 may be water,oil (mineral oil, PTFE-oil or similar) or another liquid. Theutilization of oil is appropriate in order to also lubricate thebearings 7 and 8 and the toothed wheels 3. Separate supply of coolingagent and lubricating agent, as well as corresponding gaskets, canthereby be eliminated. The only need being a controlled supply of oil tothe bearings 7 and 8.

The described solutions permit beneficial selection of raw material. Forexample, the rotors 5 and the housing 4 may consist of relativelyinexpensive aluminum materials. The proposed cooling and, mostimportantly, the uniform cooling of pump 1 have the effect that, evenwith variable operating temperatures and relatively small gaps, playdoes not consume local clearance which will result in rotor to rotorcontact and/or rotor to housing contact. Further gap reduction ispossible if materials are employed for the internal, thermally morestressed components of pump 1 (rotors, bearings, bearing supports,toothed wheels) which have a lower thermal expansion coefficient thanthe material for housing 4, which is less thermally stressed.

A moderate equilization of the expansion of all components of pump 1 isobtained as a result thereof. An exemplary selection of such material issteel, for example nickel chromium (CrNi) steel, for the interiorcomponents and aluminum for the housing. Bronze, brass or nickel silver(China or German silver) may also serve as materials for the interiorcomponents.

In an exemplary embodiment of the present invention according to FIG. 2,the interior cooling of rotor 5 comprises a cooling bushing 51, whichsupports itself, on the bearing side on housing 4 and which projectsinto hollow space 31. The cooling bushing 51 surrounds the shaft 6,which is no longer designed hollow. It traverses the hollow space (31)and carries rotor 5 in the region of its suction-sided end. Forsupplying the cooling bushing 51 with cooling agent, one or severalcooling channels 52 are provided, which are supplied by the coolingagent pump 36 in a manner not shown in more detail.

In order that the cooling bushing 51 will absorb as much heat aspossible from rotor 5, a gap 53 between cooling bushing 51 and rotor 5is selected as small as possible. In this region, the bushing 51 isequipped with threading 54, which has a pumping effect directed in thedirection of the compression chamber. Dirt particles present there areheld back.

A gap 55 between bushing 51 and shaft 6 is also relatively small inorder to produce, with the aid of threading 56, a pumping effect on theinterior side of bushing 51. Said pumping effect acts in the directionof gasket 27/bearing 7 and keeps oil particles out of the compressionchamber.

Having thus described the preferred embodiment, the invention is nowclaimed to be:
 1. A cooled screw vacuum pump, having a suction side anda pressure side, comprising a housing and two rotating systems, eachsystem comprising a screw rotor, a shaft, mutually spaced bearings oneach shaft supporting the rotors in a cantilever fashion, the bearingsbeing disposed on the same side of the rotors, and a cavity defined ineach rotor, open on the bearing side, within which cavity there isrespectively located a cooling element which cools the rotor internally,the bearing closest to the rotor being located outside the cavity in therotor.
 2. The pump according to claim 1 wherein the cavity extends atleast halfway through the entire rotor.
 3. The pump according to claim 1wherein the rotor is segmented and includes a suction-side segment and apressure-side segment joined to the suction-side segment, thepressure-side segment being hollow and the suction-side segment having aprojection received in the hollow of the pressure side segment, thecavity being defined in the hollow of the pressure side segment adjacentthe suction-side segment and being open on the bearing side.
 4. The pumpaccording to claim 3 wherein the shaft is hollow and is connected withthe rotor in fluid communication with the cavity.
 5. The pump accordingto claim 4 wherein the hollow shaft and the pressure-side segment areintegral.
 6. The pump according to claim 4 further including a coolingpipe disposed in the hollow shaft with a discharge end at the cavity. 7.The pump according to claim 6 wherein the cooling pipe supplies acooling agent to the cavity and further including an annular spacedefined between the hollow shaft and the cooling pipe for dischargingthe cooling agent from the cavity.
 8. The pump according to claim 7wherein a narrowed region is provided in the bearing-side end of theannular space between the hollow shaft and the cooling pipe.
 9. The pumpaccording to claim 7 wherein the cooling pipe is of a material havingpoor thermal conductivity.
 10. The pump according to claim 1 wherein thecavity includes an annular space between the shaft and the rotor andfurther including: a cooling bushing supported on the housing and whichextends into the annular space.
 11. The pump according to claim 10wherein the cooling bushing includes a first set of channels throughwhich a cooling agent flows.
 12. Pump according to one of the precedingclaims, characterized in that in the wall of the housing (4) of pump(1), i.e. at the level of the rotor (5), channels (41) are provided,through which flows a cooling agent.
 13. The pump according to claim 12further including: in a region of the housing encasing the bearings, athird set of channels through which the cooling agent flows.
 14. Thepump according to claim 13 wherein the shaft is hollow and is connectedwith the rotor in fluid communication with the cavity and furtherincluding: a cooling pipe disposed in the hollow shaft with a dischargeend at the cavity; and a cooling agent pump with an inlet incommunication via a conductor system with a cooling agent sump locatedin the pump housing and with an outlet in communication with at leastone of the cooling pipe, the first set of channels, the second set ofchannels, and the third set of channels.
 15. The pump according to claim14 wherein the sump and the conductor system are designed in suchfashion that the inlet of the cooling agent pump is in communicationwith the sump, both in horizontal as well as in vertical positions ofthe pump.
 16. The pump according to claim 10 wherein the cooling bushingincludes external threading which performs a pumping action directed inthe direction of a compression chamber.
 17. The pump according to claim10 wherein the cooling bushing includes internal threading whichperforms a pumping action directed in the direction of the adjacentbearing.
 18. Pump according to one of the preceding claims,characterized in that the cooling agent flowing through the pump (1) isidentical with the lubricating agent for the bearings (7, 8).
 19. Thepump according to claim 1 further including: a first set of channelsthrough a wall of the housing adjacent the rotors through which acooling agent flows.
 20. The pump according to claim 19 furtherincluding: in a region of the housing encasing the bearings, a secondset of channels through which the cooling agent flows.
 21. The pumpaccording to claim 20 wherein the shaft is hollow and is connected withthe rotor in fluid communication with the rotor cavity and furtherincluding: a cooling agent pump with an inlet in communication via aconductor system with a cooling agent sump located in the pump housingand with an outlet in communication with at least one of a cooling pipedisposed in the hollow shaft with a discharge end at the cavity, thefirst set of channels, and the second set of channels.
 22. The pumpaccording to claim 21 wherein the sump and the conductor system aredesigned in such fashion that the inlet of the cooling agent pump is incommunication with the sump, both in horizontal and vertical positionsof the pump.
 23. The pump according to claim 1, wherein each rotorincludes a suction-side segment and a pressure-side segment having asmaller diameter than the suction-side segment.
 24. The pump accordingto claim 1, wherein the cooling element includes cooling fluid whichcontacts an inner surface of the cavity directly.
 25. A cooled screwvacuum pump, having a suction side and a pressure side, comprising ahousing that defines a pumping chamber and two rotating systems, eachrotating system comprising: a screw rotor, a shaft connected at one endto the screw rotor and extending out of the pumping chamber, at leasttwo mutually spaced bearings on each shaft supporting the screw rotorsin a cantilevered fashion in the pumping chamber, all bearings being onthe same side of the rotor, and a cavity defined in each rotor, open onthe bearing side, within which cavity there is respectively located acooling fluid which cools the rotor internally, each rotor including asuction-side threaded segment and a pressure-side threaded segment withdifferent thread profiles, the depth of the thread profile of thepressure-side segment being small than the depth of the thread profileof the suction-side segment.
 26. The pump according to claim 2, whereinthe pressure-side segment of the rotor has a smaller diameter than thesuction-side segment.
 27. A cooled screw vacuum pump having a suctionside and a pressure side, the vacuum pump further including: a housingand two rotating systems, each rotating system including a screw rotor,a shaft, and mutually spaced bearings on each shaft supporting therotors; each rotor defining a cavity open on a bearing side, withinwhich cavity there is respectively: a cooling element located in thecavity which cools the rotor internally; a first helical pumping chamberdefined in the housing; a second helical pumping chamber with a reducedcross section relative to the first pumping chamber extending from thefirst pumping chamber to an outlet passage; a bore extending from theoutlet passage to an end of the first pumping chamber adjacent thesecond pumping chamber; and a non-return valve mounted to the bore tolimit flow to a direction from the first pumping chamber to the outlet.28. An evacuation apparatus comprising: a housing having an inlet portand an outlet port; a pump section arranged in said housing and having asuction side and an exhaust side, the pump section includinginterengaging rotors, each of the rotors having at least one threadedportion, the threaded portions, together with said housing, defining agas-transporting space, each rotor further including a cooling cavitydefined in and opening only to an exhaust-side portion of the rotor; ameans for circulating a cooling fluid flow through each cavity to coolthe rotors internally; a rotating shaft connected to the exhaust-sideportion of each rotor; bearings supporting the rotating shafts in acantilever fashion, the bearings being axially spaced apart from thethreaded portions, all on the same side of the rotor, and fliaidicallyisolated from the cooling fluid flow circulating through the coolingcavity; and at least one motor for rotating the interengaging rotors.29. A cooled screw vacuum pump, having a suction side and a pressureside, the pump comprising a housing and two rotating systems, eachrotating system comprising: a rotor with a thread, the threads of therotors and the inside of the housing acting together, when the rotorsare rotating, to transport a gas from the suction side to the pressureside; a hollow shaft supporting the rotor; mutually spaced bearings onthe shaft, all bearings being situated at the pressure side of therotor; each rotor being provided with a cavity open only to the pressureside, the bearing closest to the rotor being located outside the cavity,a cooling pipe extending axially through the hollow shaft forming afirst channel in fluid connection with the cavity in the rotor; and, thecooling pipe and the hollow shaft forming a second channel surroundingthe cooling pipe and in fluid connection with the cavity in the rotor.30. The pump according to claim 29, wherein the first channel supplies acooling agent to the cavity and the second channel discharges thecooling agent from the cavity.
 31. The pump according to claim 30,further including a narrowed region is defined in a bearing-side end ofthe second channel.
 32. The pump according to claim 31, wherein thecooling pipe is of a material having poor thermal conductivity.
 33. Thepump according to claim 29, wherein the cooling agent flowing throughthe pump is identical with a lubrication agent for the bearings.
 34. Thepump according to claim 29, wherein the rotor cavity extends at leasthalfway through the entire rotor.
 35. A fluid cooled screw vacuum pumpcomprising: a housing defining a pumping chamber and a coolant chamberwhich are fluidically isolated from each other, the housing defining asuction inlet into the pumping chamber and a pressure outlet from thepumping chamber; and a pair of rotating systems each including: at leasttwo bearings mounted to the housing in the coolant chamber; a shaftrotatably mounted in the bearings with one end extending cantileveredinto the pumping chamber; a threaded screw rotor connected to the oneend of the shaft, the screw rotor being supported only by the shaft in acantilevered fashion in the pumping chamber, the screw rotors of thepair of rotating systems intermeshing to pump gas from the suction inletto the pressure outlet; and a cavity defined in the shaft and the screwrotor in fluid communication with coolant chamber through which cavitycoolant fluid is passed to cool the screw rotor internally.
 36. A cooledscrew vacuum pump, having a suction side and a pressure side, comprisinga housing and two rotating systems, each rotating system comprising: arotor with a thread, the threads of the rotors and the inside of thehousing acting together, when the rotors are rotating, to transport agas from the suction side to the pressure side, the rotor beingsegmented and including a suction-side segment and a pressure-sidesegment joined to the suction-side segment; a hollow shaft supportingthe rotor; mutually spaced bearings on the shaft, all bearings beingsituated at the pressure side of the rotor; each pressure-side segmentbeing provided with a cavity adjacent the suction-side segment and opento the pressure side; the bearing closest to the rotor being located onthe pressure side outside the cavity; a cooling agent, contacting aninner surface of the cavity directly; a cooling pipe extending axiallythrough a central opening of the hollow shaft, the inner surface of thecooling pipe forming a first channel in fluid connection with the cavityin the rotor, the central opening of the hollow shaft and the pipeforming a second channel surrounding the pipe, being annular and influid connection with the cavity in the rotor.
 37. The pump according toclaim 36, wherein the hollow shaft and the pressure-side segment areintegral.
 38. The pump according to claim 36, wherein the pressure-sidesegment has a smaller diameter than the suction-side segment.
 39. Thepump according to claim 36, wherein the suction-side segment and thepressure-side segment are threaded with different thread profiles, adepth of the thread profile of the pressure-side segment being smallerthan a depth of the thread profile of the suction-side segment.
 40. Thepump according to claim 36, wherein the first channel supplies thecooling agent to the cavity and the second channel discharges thecooling agent from the cavity.
 41. The pump according to claim 40,wherein a narrowed region is defined in a bearing-side end of the secondchannel.
 42. The pump according to claim 41, wherein the cooling pipe isof a material having poor thermal conductivity.
 43. The pump accordingto claim 36, wherein the cooling agent flowing through the pump isidentical with a lubrication agent for the bearings.
 44. The pumpaccording to claim 36, wherein the cavity extends at least halfwaythrough the rotor.
 45. A cooled screw vacuum pump, having a suction sideand a pressure side, comprising a housing and two rotating systems, eachrotating system comprising: a rotor with a thread, the threads of therotors and the inside of the housing acting together, when the rotorsare rotating, to transport a gas from the suction side to the pressureside; a hollow shaft supporting the rotor; mutually spaced bearings onthe shaft, all bearings being situated at the pressure side of therotor; each rotor being provided with a cavity open to the pressureside; the bearing disposed closest to the rotor being located outsidethe cavity; a cooling pipe extending axially through the hollow shaft,an inner surface of the cooling pipe forming a first channel in fluidconnection with the cavity for supplying a cooling agent to an innersurface of the cavity directly in the rotor; and a central opening ofthe shaft and the pipe forming a second, annular channel surrounding thepipe, in fluid connection with the cavity in the rotor, and, a first setof channels through a wall of the housing adjacent the rotors throughwhich the cooling agent flows.
 46. The pump according to claim 45,further including: in a region of the housing encasing the bearings, asecond set of channels through which the cooling agent flows.
 47. Thepump according to claim 46, further including: a cooling agent pump withan inlet in communication via a conductor system with a cooling agentsump located in the pump housing and with an outlet in communicationwith at least one of the cooling pipe disposed in the hollow shaft witha discharge end at the cavity, the first set of channels, and the secondset of channels.
 48. The pump according to claim 47, wherein the sumpand the conductor system are designed in such fashion that the inlet ofthe cooling agent pump is in communication with the sump, both inhorizontal and vertical positions of the pump.
 49. The pump according toclaim 45, wherein the first channel serves to supply the cooling agentto the cavity and the second channel serves to discharge the coolingagent from the cavity.
 50. The pump according to claim 49, wherein anarrowed region is provided in the bearing-side end of the secondchannel.
 51. The pump according to claim 50, wherein the cooling pipe isof a material having poor thermal conductivity.
 52. The pump accordingto claim 45, wherein the cooling agent flowing through the pump is alsoa lubrication agent flowing over the bearings.
 53. The pump according toclaim 45, wherein the cavity extends at least halfway through the rotor.